An industrial motor widely used as a rotative drive source for machine tools and other industrial machines has a construction including a laminated stator core with an outer circumference serving as the casing for the motor, a stator formed by inserting excitation coils in the laminated stator core, a front housing joined to the front end of the laminated stator core, a rear housing joined to the rear end of the laminated stator core, rotary bearings fitted in holes in the front and rear housings, and a rotor supported for rotation in the rotary bearings within the bore of the stator, with a gap between the outer circumference of the rotor and the inner circumference of the stator.
Such an industrial motor is formed, by taking into consideration that the industrial motor is mostly subjected to severe running conditions due to a continuous long operation thereof, in a construction having sufficient mechanical strength by forming the principal components from metal, particularly, the front and rear housings joined respectively to the front and rear ends of the stator core, in addition a means for transmitting and dispersing heat generated by copper loss and iron loss when an electric drive current is supplied to the exciting coils is incorporated to thereby prevent damage to and a reduction in the life of the motor due to an increase in the temperature of the motor to a high level. A motor having a greater output generates a greater amount of heat, and thus a metallic housing having a high heat conductivity is essential to a large-capacity industrial motor, so as to prevent burning the excitation coils. On the other hand; power, i.e., the excitation current, is supplied to an industrial motor having such a metallic housing, in, most cases, by electrically connecting an electrical connector (for example, a male electric connector) at the extremity of a power supply cable to a female electric connector screwed to a connector base projecting outward from a portion of the metallic rear housing of the motor.
FIG. 4 shows an example industrial motor provided with a conventional housing structure. This conventional industrial motor is constructed by joining a metallic front flange 3 and a rear housing 4 respectively to the front and rear ends of the core 2 of a stator 1, disposing a rotor (not shown) inside the stator 1 with its output shaft 5 projecting to the front from the front flange 3 so as to be connected mechanically to a driven member by a coupling or the like, and joining a cover 6 to the rear end of the rear housing 4 so as to cover the rear end of the motor. A connector base 7 is formed on the rear housing 4 so as to protrude radially outward from the outer circumference of the rear housing 4. An off-the-shelf electrical connector 8 is fastened to the connector base 7 by screws 9.
Such a construction provided with the electrical connector screwed to the connector base of the metallic housing requires a process for attaching the electrical connector 8 to the connector base 7 using screws 9 by hand during the fabrication of the motor.
Furthermore, when the motor is intended for use as the rotative drive source of a machine tool, a packing 9' is placed between the electric connector 8 and the connector base 7 to prevent wetting the interior of the motor with machining liquid splashed out during the operation of the machine tool. The electrical connector 8 is fastened to the connector base 7 by the screws 8, and then the junction of the electric connector 8 and the connector base 7 is coated with a sealing grease to prevent moisture leakage into the motor. Thus, the motor manufacturing process requires an excessive amount of work, which is an impediment to any desired cost reduction.
Furthermore, although the construction having the connector base 7 projecting from the outer circumference of the metallic rear housing 4 is intended to reduce costs through the employment of the available electrical connector 8, the connector base 7 radially projecting from the outer circumference of the housing increases the overall size of the enveloping surface of the motor including the top of the connector base 7. Thus, the motor requires a relatively large space for installation on a machine tool or the like.
On the other hand, the conditions for dispersing heat generated by copper loss and iron loss are not very severe with an industrial motor having a comparatively small output capacity. The rear housing need not necessarily be formed from metal but may be formed from a resin, in view of forming a motor having a lightweight construction, provided that only the front flange is formed from metal, to ensure satisfactory heat conduction and sufficient mechanical strength for supporting the output shaft and for coupling the output shaft and the driven member.